Wouldn't the seperation distance be up to whoever dictates LPG codes?? Doesn't seem like an issue for an electrician. Your work will satisfy code, why should you have to worry about where someone else set the tank??. In Maine, I'd start with the Maine Oil Dealers assoc. or the company who set the tank. Also in Maine one must be licensed to set propane tanks

WalrusThe separation is dictated by Fire Code....The NEC is dictated by Fire Code.

I was installing power to Propane Pump Station for the pump and a Night Light at a local Mini-Mart and could not find the code in the NEC book. I found it in the local County Code. Its been so long since I've seen it I cant recall the the artilce, but itwas "cut and paste" from Fire Code. There is a 10'-00" envelope that follows the contour of the tank, anything inside or passes through that area is Class 1 Div 1.